The present invention in a preferred implementation relates to improvements in radio data communication systems wherein a number of mobile transceiver units are to transmit data to a number of base stations under a wide range of operating conditions. The invention is preferably to be applicable as an upgrade of an existing data capture system wherein a number of hand-held transceiver units of an earlier design are already in the field representing a substantial economic investment in comparison to the cost of base stations, accessories and components. In installations spread over an extensive area, a large number of mobile portable transceiver units may be employed to gather data in various places and multiple base stations may be required. In a variety of such installations such as warehouse facilities, distribution centers, and retail establishments, it may be advantageous to utilize not only multiple bases capable of communication with a single host, but with multiple hosts as well.
An early RF data collection system is shown in Marvin L. Sojka, U.S. Pat. No. 4,924,462 assigned to the assignee of the present application. This patent illustrates (in the sixth figure) a NORAND® RC2250 Network Controller which supports one base transceiver for communication with multiple mobile portable transceivers. The exemplary prior art device is capable of communicating with a host computer through an RS232C interface at up to 19,200 baud in asynchronous mode. In order for an optional RS422 interface to be substituted for an RS232C interface, the unit must be opened and substitute circuitry components installed within it.